﻿258 
  J. 
  W. 
  JtTDD 
  ON 
  THE 
  SECONDARY 
  ROCKS 
  OP 
  SCOTLAND. 
  

  

  of 
  the 
  "Western 
  Isles 
  give 
  rise, 
  owing 
  to 
  their 
  peculiar 
  modes 
  of 
  

   weathering. 
  Acted 
  upon 
  very 
  slowly 
  by 
  the 
  agents 
  of 
  atmospheric 
  

   disintegration, 
  the 
  rock-surfaces 
  assume 
  a 
  remarkable 
  roughness 
  

   owing 
  to 
  the 
  persistence 
  of 
  the 
  crystals 
  of 
  diallage 
  and 
  augite, 
  ac- 
  

   quiring 
  at 
  the 
  same 
  time 
  a 
  deep 
  brown 
  tint 
  from 
  the 
  peroxidation 
  of 
  

   the 
  iron 
  ; 
  and, 
  moreover, 
  these 
  surfaces, 
  not 
  giving 
  rise 
  to 
  the 
  form- 
  

   ation 
  of 
  soil, 
  are 
  altogether 
  destitute 
  of 
  any 
  covering 
  of 
  vegetation. 
  

   The 
  lower 
  flanks 
  of 
  the 
  mountains 
  are 
  marked 
  by 
  the 
  dome-shaped 
  

   forms 
  resulting 
  from 
  the 
  passage 
  over 
  them 
  of 
  glaciers 
  ; 
  and 
  the 
  

   grooving 
  and 
  striation 
  are 
  wonderfully 
  preserved 
  upon 
  them*; 
  but 
  

   the 
  summits 
  of 
  the 
  same 
  mountains 
  stand 
  up 
  in 
  the 
  form 
  of 
  wild 
  

   craggy 
  pinnacles, 
  many 
  of 
  which 
  are 
  altogether 
  inaccessible. 
  More- 
  

   over 
  the 
  striking 
  features 
  of 
  these 
  rugged 
  and 
  barren 
  rocks 
  are 
  height- 
  

   ened 
  by 
  the 
  contrasts 
  which 
  they 
  present 
  with 
  the 
  verdant, 
  terraced 
  

   slopes 
  of 
  the 
  basaltic 
  plateaux 
  on 
  the 
  one 
  hand, 
  and 
  the 
  smooth, 
  

   dome-shaped 
  and 
  debris 
  -covered 
  hills 
  of 
  granite 
  on 
  the 
  other. 
  

  

  These 
  features 
  of 
  the 
  gabbro 
  rocks 
  are 
  displayed 
  in 
  a 
  sufficiently 
  

   striking 
  manner 
  in 
  Mull, 
  especially 
  in 
  the 
  wild 
  gien 
  between 
  Beinn 
  

   Buy 
  and 
  Creach 
  Beinn, 
  and 
  also 
  in 
  Ardnamurchan 
  and 
  Bum 
  ; 
  but 
  

   in 
  each 
  of 
  these 
  cases 
  the 
  entangled 
  portions 
  of 
  acid 
  rocks 
  give 
  rise 
  

   to 
  the 
  formation 
  of 
  streams 
  and 
  taluses 
  of 
  detritus 
  and 
  the 
  conse- 
  

   quent 
  production 
  of 
  soil 
  and 
  vegetation, 
  relieving 
  the 
  monotonous 
  

   barrenness 
  of 
  the 
  surfaces 
  of 
  these 
  rocks. 
  But 
  in 
  the 
  island 
  of 
  

   Skye 
  we 
  have 
  a 
  considerable 
  area 
  which 
  -is 
  formed 
  almost 
  exclu- 
  

   sively 
  of 
  the 
  gabbro 
  rocks; 
  and 
  the 
  wonderful 
  features 
  of 
  the 
  

   scenery 
  to 
  which 
  these 
  give 
  rise 
  are 
  familiar 
  to 
  all 
  who 
  have 
  

   visited 
  the 
  Cuchullin 
  Hills 
  and 
  Blabheinn, 
  being 
  most 
  remarkably 
  

   ^displayed 
  in 
  the 
  sombre 
  glen 
  which 
  contains 
  the 
  "dark 
  loch" 
  of 
  

   doruiskh. 
  

  

  The 
  deep 
  impression 
  made 
  by 
  this 
  remarkable 
  scene 
  on 
  the 
  mind 
  

   of 
  Sir 
  Walter 
  Scott 
  is 
  recorded 
  in 
  his 
  well-known 
  lines 
  in 
  the 
  ' 
  Lord 
  

   of 
  the 
  Isles 
  ' 
  : 
  — 
  

  

  " 
  Barely 
  human 
  eye 
  has 
  known 
  

  

  A 
  scene 
  so 
  stern 
  as 
  that 
  dread 
  lake, 
  

   With 
  its 
  dark 
  ledge 
  of 
  barren 
  stone. 
  

  

  Seems 
  that 
  primeval 
  earthquake's 
  sway 
  

  

  Has 
  rent 
  a 
  strange 
  and 
  shattered 
  way 
  

   Through 
  the 
  rude 
  bosom 
  of 
  the 
  hill, 
  

  

  And 
  that 
  each 
  naked 
  precipice, 
  

  

  Sable 
  ravine, 
  and 
  dark 
  abyss, 
  

   Tells 
  of 
  the 
  outrage 
  still/' 
  

  

  But 
  for 
  the 
  geologist 
  this 
  justly 
  celebrated, 
  and 
  now 
  tourist- 
  

   haunted, 
  locality 
  may 
  claim 
  a 
  more 
  especial 
  interest. 
  For 
  if 
  his 
  

   study 
  of 
  the 
  rocks 
  dispels, 
  as 
  it 
  certainly 
  will 
  do, 
  the 
  poet's 
  beautiful 
  

   dream 
  concerning 
  their 
  origin, 
  it 
  will 
  be 
  only 
  to 
  replace 
  it 
  by 
  a 
  far 
  

   grander 
  conception 
  ; 
  and 
  as 
  he 
  stands 
  here, 
  in 
  the 
  very 
  centre 
  of 
  

   the 
  cooled 
  reservoir 
  of 
  an 
  ancient 
  volcano, 
  his 
  instructed 
  imagination 
  

   will 
  revel 
  in 
  the 
  reconstruction 
  from 
  reliable 
  data 
  of 
  the 
  wild 
  and 
  

   grand 
  features 
  cf 
  this 
  old 
  " 
  Tierra 
  del 
  Fuego." 
  

  

  * 
  Vide 
  J. 
  D. 
  Forbes, 
  Edinb. 
  New 
  Phil. 
  Journ. 
  New 
  Ser. 
  vol. 
  xl. 
  pp. 
  90-99 
  

   (1845-46). 
  

  

  